exercism 82 Linked List

Author: kumar91gopi

README.md

@@ -307,6 +307,7 @@ solution of many challenges of [Leetcode](https://leetcode.com/), [Exercism](htt
 79. [Rotational Cipher](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/rotational_cipher.rb)
 80. [Largest Series Product](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/largest_series_product.rb)
 81. [Prime Factors](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/prime_factors.rb)
+82. [Linked List](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/linked_list.rb)
 
 <a name="leetcode"/>
 

exercism/linked_list.rb

@@ -0,0 +1,46 @@
+# Problem : https://exercism.org/tracks/ruby/exercises/linked-list
+
+#Solution
+class Deque
+    NODE = Struct.new(:val,:prev,:next)
+
+    def initialize
+      @head = nil
+      @tail = @head
+    end
+
+    def push(element)
+      if @tail.nil?
+        @head = @tail = NODE.new(element,nil,nil)
+        return
+      end
+      last_node = @tail
+      last_node.next = NODE.new(element,last_node,nil)
+      @tail = last_node.next
+    end
+    def pop
+
+      unless @tail.nil?
+        last_node = @tail
+        @tail = @tail.prev
+        return last_node.val
+      end
+    end
+
+    def shift
+      first_val = @head.val
+      @head = @head.next
+      @tail = nil if @head.nil?
+      first_val
+    end
+
+     def unshift(element)
+      new_node = NODE.new(element, nil, @head)
+      @head.prev = new_node unless @head.nil?
+      @head = new_node
+      @tail = new_node if @tail.nil?
+    end
+  end
+
+  # Solution (one liner)
+  class Deque < Array; end     # As array class has all the functionalities in Ruby